Ethylene/α-olefin rubbers and ethylene/α-olefin/non-conjugated diene copolymer rubbers have no unsaturated bond in the main chain, and therefore, they are excellent in weathering resistance, heat resistance and ozone resistance as compared with conjugated diene type rubbers. Taking advantage of these properties, rubber compositions containing such copolymer rubbers, crosslinked products of the compositions and foamed products of the compositions have been broadly used for parts of automobile industry, industrial rubber articles, electrically insulating materials, civil engineering and construction materials, rubber articles such as rubberized fabric, etc.
For example, a rubber composition for injection molding sponge, which contains an ethylene/α-olefin/non-conjugated polyene copolymer rubber, a crystalline polyolefin resin and a blowing agent, is known (see, for example, patent document 1).
Further, a rubber composition containing an ethylene/α-olefin/non-conjugated polyene copolymer rubber, a polyolefin resin and a blowing agent, and a rubber foamed product obtained by crosslinking and foaming a rubber composition containing an ethylene/α-olefin/non-conjugated polyene copolymer rubber and a synthetic resin are also known (see, for example, patent documents 2 and 3).
Molded products obtained from these compositions and the above-mentioned rubber foamed product are excellent in hardness, etc., but they are insufficient in compatibility of the ethylene/α-olefin/non-conjugated polyene copolymer rubber with other resins (polyolefin resin, synthetic resin, etc.), and there is yet room for improvement.
Crosslinked rubbers comprising a copolymer rubber composed of ethylene and an α-olefin of 3 to 20 carbon atoms and/or a non-conjugated polyene have been favorably applied to uses requiring environmental resistance, such as weatherstrips and water hoses for automobiles, in the past. In the compounding for such rubbers, a large amount of a softener is generally used together with a reinforcing agent and a filler. For automobiles for which lengthening of life will be required more and more in the future, weatherstrips and water hoses capable of withstanding long-term use and maintaining initial performance become necessary, and therefore, crosslinked rubbers exhibiting more excellent environmental resistance than before have been desired.
Such crosslinked rubbers, however, have problems of fogging and tackiness caused by a low-molecular weight component of the softener. The “fogging” is a phenomenon that when a crosslinked rubber is used as an interior skin material of a weatherstrip, an instrument panel or the like of an automobile, a door glass, a front glass, etc. are fogged by the low-molecular weight component evaporated from such a part, and the “tackiness” is a phenomenon that the low-molecular weight component blooms on the surface of an interior skin material of a weatherstrip, an instrument panel or the like of an automobile to cause tacky surface.
For example, there is disclosed, in a patent document 4, a rubber composition that has become excellent in weathering resistance, heat resistance and low-temperature flexibility by adding a softener (copolymer of ethylene and an α-olefin of 3 to 20 carbon atoms) having a number-average molecular weight of 400 to 2000, a pour point of not higher than −25° C. and a viscosity index of not less than 120, but problems of fogging and tackiness have not been solved yet.    Patent document 1: Japanese Patent Laid-Open Publication No. 195227/1998    Patent document 2: Japanese Patent Laid-Open Publication No. 256095/2002    Patent document 3: Japanese Patent Laid-Open Publication No. 212328/2002    Patent document 4: Japanese Patent Laid-Open Publication No. 11255/2001